The present invention relates to epoxy acrylates of higher molecular weight and to novel carboxyl group-containing epoxy acrylates of higher molecular weight, to the preparation thereof, to the use of said epoxy acrylates in photoresist formulations, and to the use of said formulations, in particular in the field of printed wiring boards, typically as solder resists or as primary resists (etch resists or galvanoresists), and of printing plates.
Epoxy acrylates are known in abundance and are also used, inter alia, in compositions used as photoresist formulations.
Formulations for solder resists that contain reaction products of epoxy novolak resins with acrylic acid and cyclic carboxylic anhydrides are disclosed, inter alia, in EP 0 273 729. They are developable in aqueous alkaline media and have good thermal resistance and photosensitivity. Their resistance to chemicals, however, is unsatisfactory.
EP 0 418 011 discloses compositions for solder mask that are likewise based on reaction products of epoxy cresol novolaks with acrylic acid and cyclic dicarboxylic anhydrides, using 0.4 to 0.9 equivalent of acrylic acid per equivalent of epoxy group, such that the final product simultaneously contains acid and epoxy groups in the same molecule. A second thermal crosslinking reaction between these two functionalities is thereby made possible in the application of these resist compositions. The problem here is, however, aside from the preparation of the products (danger of gelation in the reaction with the anhydride), the storage stability, as the formulation containing such reaction products has a certain reactivity even at room temperature. All these cited epoxy acrylates are quite generally relatively low-molecular.
Photochemically or thermally cured epoxy acrylates that are derived from low molecular epoxy resins and epoxy novolaks are known for their good thermal and mechanical properties as well as for their good resistance to aggressive chemicals. However, the tackiness and edge coverage of the resist films obtained with these systems on conductors owing to the fairly low relative molar mass are unsatisfactory. In practical application it is therefore often necessary to avoid these shortcomings by adding highly polymerised polymer binders. Such binders normally contain no functional acrylate groups and do not react concurrently during the photochemical or thermal cure, i.e. they are not incorporated as xe2x80x9cpassivexe2x80x9d components in the network and therefore result in a dilution of the network density, which, in turn, adversely affects in particular the resistance to chemicals and the electrical properties of processed resist layers. Furthermore, the photosensitivity decreases as a consequence of the xe2x80x9cdilutionxe2x80x9d of the acrylate groups. The addition of highly polymerised polymer binders induces high viscosity of these formulations even if the solids content is relatively low and therefore often results in serious problems in coating.
It is therefore the object of this invention to provide acrylates that do not have the shortcomings referred to above.
This object is achieved in the practice of this invention by epoxy acrylates and novel carboxyl group-containing epoxy acrylates of higher molecular weight, which, when used in resist formulations, are able to function without or with only minor amounts of additional polymer binders. They are obtained by reaction of so-called xe2x80x9cpostglycidylatedxe2x80x9d epoxy resins (PGER) with, typically, (meth)acrylic acid.
Batzer and Zahir (J. Appl. Polym. Sci., 19, 609 (1975)) describe the postglycidylation of a low molecular liquid diglycidyl ether of bisphenol A. U.S. Pat. No. 4,623,701 discloses postglycidylated epoxy resins and the cure thereof with various epoxy hardeners; and U.S. Pat. No. 4,074,008 discloses photocrosslinked epoxy resins containing more than 2 epoxy groups in the molecule, at least 2 of which originate from a postglycidylation reaction. The photocrosslinkable groups in the molecular chain constitute xcex1,xcex2-unsaturated carbonyl systems (chalcone groups). Derivatives containing (meth)acrylyl groups are not described therein.
It is also known that the photosensitivity of an xcex1,xcex2-unsaturated carbonyl system that is photocrosslinkable by a 2+2-cycloaddition mechanism is substantially lower compared with the photopolymerisation of acrylates.
Japanese patent Kokai Hei 04-294352 discloses the modification of epoxy-novolak resins by reaction with an unsaturated monocarboxylic acid and subsequently with an unsaturated anhydride of a polycarboxylic acid and the use thereof in photosensitive aqueous formulations. Furthermore, European patent application 0 292 219 discloses photosensitive systems that contain epoxy compounds of bisphenol A that are modified with acrylic acid.
Specifically, the invention provides novel epoxy acrylates of formula III 
wherein
Q is hydrogen or a group of formula 
R1 is xe2x80x94H or xe2x80x94CH3, R2 is xe2x80x94H, xe2x80x94CH3 or phenyl
T is the radical of an aromatic bifunctional compound, and
M is each independently hydrogen or a group of formula 
in which
R1 and R2 are as defined above,
A is the radical of an aromatic bifunctional compound,
n is an integer from 0 to 300, and
L is a group of formula 
xe2x80x83or xe2x80x94Oxe2x80x94Axe2x80x94OM,
with the proviso that, in formula III, not all radicals M may simultaneously be hydrogen or a group of formula 
but at least 10 mol %, preferably 20-100 mol %, of the radicals M that are not present in the end groups Q and L denote a group of the above formula 
The epoxy acrylates of formula III are obtained by reacting a postglycidylated epoxy resin of formula II 
wherein
E is hydrogen or a group of formula 
F represents the groups of formula xe2x80x94Oxe2x80x94Axe2x80x94OG or 
G is xe2x80x94H or the radical 
as in formula III, at least 10 mol % of the radicals G in formula II that are not present in the end groups E and F, represent the group of formula 
A, T, and n have the given meanings,
with an ethylenically unsaturated monocarboxylic acid in the presence of a catalyst and a polymerisation inhibitor, at elevated temperature.
If n in formula III is 0, then Q is xe2x80x94H and L is the group of formula 
In preferred epoxy acrylates of formula III, n is an integer from 0 to 50, preferably from 0 to 30, and the symbols A and T have the preferred meanings of A and B given in Japanese patent Kokai Hei 1-195056.
Preferred bifunctional aromatic compounds A and T are linking groups of formulae 
in which R4 and R5 are each independently of the other xe2x80x94H or C1-C4alkyl, Z is xe2x80x94Sxe2x80x94, xe2x80x94Oxe2x80x94 or xe2x80x94SO2, and the aromatic radicals of the linking group A or T are unsubstituted or substituted by halogen or C1-C4alkyl. C1-C4 Alkyl is preferably xe2x80x94CH3 and halogen is preferably bromo.
Particularly preferred linking groups A and T each independently of the other have the formula 
wherein R4 and R5 are as defined above and the phenyl radicals of the linking group are unsubstituted or substituted by bromo, and, preferably have the formulae 
Throughout this specification, epoxy acrylates are taken to mean reaction products of epoxy compounds with (meth)acrylic acid.
Some of the postglycidylated epoxy resins of formula II are known and are prepared from the corresponding known advanced epoxy resins of formula I 
by a glycidylation reaction, wherein in formula I
U is hydrogen or the group of formula 
D is the group of formula 
or the radical xe2x80x94Oxe2x80x94Axe2x80x94OH, and the symbols A, T and n are as defined in connection with formula III.
The advanced epoxy resins of formula I on the other hand are obtained by known polyaddition of a bisphenol of formula
HOxe2x80x94Axe2x80x94OH 
to a diepoxy of formula 
wherein A and T are the radical of a bifunctional aromatic compound.
The bisphenols HOxe2x80x94Axe2x80x94OH or HOxe2x80x94Txe2x80x94OH are preferably known bisphenols, more particularly bisphenol A and tetrabromobisphenol A, as well as those that are described in Japanese patent Kokai Hei 1-195056, preferably bisphenol A, bisphenol F, tetrabromobisphenol A and tetrabromobisphenol F.
To prepare the advanced epoxy resins, an excess of the above diepoxy is used, so that the advanced epoxy resins of formula I carry epoxy end groups. It is, however, also possible to use an excess of bisphenol HOxe2x80x94Axe2x80x94OH and thus to prepare molecules carrying phenolic end groups. The molecular weight is determined by the molar ratio of bisphenol HOxe2x80x94Axe2x80x94OH to the diepoxy. If desired, it is also possible to add minor amounts of higher functional phenols or epoxy compounds (e.g. trisphenols or triepoxyphenyl compounds) to the polyaddition. Specific amounts of starting materials (bisphenol HOxe2x80x94Axe2x80x94OH and/or diepoxy compound may also be present in the advanced epoxy resin.
The advanced epoxy resins of formula I contain secondary aliphatic hydroxyl groups resulting from the addition of the phenolic hydroxyl group to the oxirane ring 
The glycidylation reaction to give the postglycidylated epoxy resins of formula II is carried out by known methods by reacting the advanced epoxy resin (I) with e.g. an excess of epichlorohydrin in the presence of a base (e.g. NaOH) and of a catalyst at elevated temperature.
The amount of base used in the glycidylation will depend on the desired degree of glycidylation. It is preferred to use 0.1 to 1.2 equivalents of base per equivalent of secondary HO group in the advanced epoxy resin. Water is removed by azeotropic distillation using excess epichlorohydrin as entrainer.
Particularly suitable catalysts are quaternary ammonium salts or phosphonium salts, typically including tetramethylammonium chloride, benzyltrimethylammonium chloride, benzyltriethylammonium chloride, tetraethylammonium chloride and tetrabutylammonium bromide.
The reaction temperature is conveniently in the range from 40 to 80xc2x0 C., preferably from 50 to 65xc2x0 C.
The aliphatic OH groups are partially or completely glycidylated by the glycidylation reaction.
The further reaction of the postglycidylated epoxy resins of formula II to the epoxy acrylates of formula III is likewise carried out in known manner by reaction with an ethylenically unsaturated monocarboxylic acid of formula 
Suitable acids typically include crotonic acid, cinnamic acid and, preferably, acrylic acid or methacrylic acid or a mixture thereof. R1 and R2 are as defined above.
It is preferred to use a catalyst in the reaction. Particularly suitable catalysts are metal salts such as chromium compounds, amines such as triethylamine or benzyldimethylamine, also ammonium salts such as benzyltrimethylammonium chloride, or also triphenylphosphine and triphenylbismuth.
A solvent may be added to the reaction, as the postglycidylated epoxy resins of formula II are in the form of solids. However, the solvent must be inert to the educt. Suitable solvents include: ketones such as acetone, methyl ethyl ketone, cyclohexanone; esters such as ethyl and butyl acetate, ethoxyethyl acetate or methoxypropyl acetate; ethers such as dimethoxyethane and dioxane; aromatic hydrocarbons such as toluene, benzene and xylenes, as well as mixtures of two or more of these solvents.
The temperature will conveniently be in the range from 80 to 140xc2x0 C., the reaction with acrylic acid being preferably carried out in the range from 80 to 120xc2x0 C. and that with methacrylic acid preferably in the range from 80 to 140xc2x0 C.
A polymerisation inhibitor may also be added to the reaction medium, suitably hydroquinone, hydroquinone monomethyl ether and 2,6-di-tert-butyl-p-cresol.
It is desirable to introduce air or a mixture of nitrogen/oxygen into the reaction medium, as some of the aforementioned polymerisation inhibitors are effective only in the presence of oxygen. Depending on the amount of ethylenically unsaturated monocarboxylic acid used, epoxy acrylates of formula II that are completely or only partially acrylated are obtained. The monocarboxylic acid can be used in equimolar amounts with respect to the epoxy groups or in less than equivalent amount. The completely reacted epoxy acrylates contain almost no more epoxy groups.
The epoxy acrylates of formula III need neither be isolated from the reaction medium nor purified. The reaction solution can be used direct as obtained in the synthesis.
The partially as well as the completely reacted products of formula III contain aliphatic hydroxyl groups originating from the reaction of the epoxy groups with the ethylenically unsaturated monocarboxylic acid. They may additionally contain aliphatic hydroxyl groups from the educt.
The completely acrylated epoxy acrylates of formula III can then be further reacted to carboxyl group-containing epoxy acrylates of formula IV 
wherein
X is hydrogen or a group of formula 
R3 is the radical of a cyclic anhydride of a polycarboxylic acid after removal of the anhydride radical,
W1 is hydrogen or a group of formula 
W2 is xe2x80x94H or the group 
Y is the group of formula xe2x80x94Oxe2x80x94Axe2x80x94Oxe2x80x94W1 or 
wherein the symbols A, T, R1, R2, R3 and n have the given meanings, with the proviso that, in formula IV, at least 10 mol % of radicals W1 that are not in the end groups X and Y are a group of formula 
R1, R2 and R3 have the given meanings.
If n in formula IV is 0, then X is hydrogen and Y is the group of the formula 
As the completely reacted epoxy acrylates of formula III contain almost no more epoxy groups, they can be reacted with cyclic anhydrides of polycarboxylic acids. In this case, the aliphatic hydroxyl groups react with the cyclic anhydride to effect ring opening and hemiester formation. In this reaction, for each reacted hydroxyl group a carboxylic acid bonded to the resin forms. The reaction comprises reacting the epoxy acrylate of formula III with the cyclic anhydride, in the absence or presence of a catalyst and of a polymerisation inhibitor, at elevated temperature. The HO groups of the compounds of formula III are completely or partially acylated, accompanied by ring opening of the anhydride. It is therefore advantageous that the epoxy acrylates contain no more epoxy groups, otherwise gelation occurs. The anhydride is used in equimolar amounts with respect to the hydroxyl groups or in a less than equivalent amount. The reaction is known per se.
Suitable anhydrides of polycarboxylic acids typically include succinic anhydride, maleic anhydride, glutaric anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, 3-methyl- and 4-methylhexahydrophthalic anhydride, 3-ethyl- and 4-ethylhexahydrophthalic anhydride, 3-methyl-, 3-ethyl-, 4-methyl- and 4-ethyltetrahydrophthalic anhydride, itaconic anhydride, phthalic anhydride, and trimellitic anhydride. Preferred anhydrides are succinic, tetrahydrophthalic, hexahydrophthalic and phthalic anhydride.
Suitable catalysts typically include amines such as triethylamine, benzyldimethylamine, pyridine or dimethylaminopyridine, or triphenylphosphine or metal salts such as chromium or zirconium compounds.
If desired, a solvent may be added to the reaction medium, as the epoxy acrylates of formula III are in the form of solids. The solvent must, however, be inert to the cyclic anhydride, so that hydroxyl group-containing solvents are not suitable. The solvents cited in connection with the reaction with the ethylenically unsaturated monocarboxylic acids may suitably be used.
The reaction temperature is conveniently in the range from 60 to 140xc2x0 C., and suitable polymerisation inhibitors are typically hydroquinone, hydroquinone monomethyl ether and 2,6-di-tert-butyl-p-cresol.
It is desirable to introduce dry air or a mixture of nitrogen/oxygen into the reaction medium. In a preferred embodiment of the invention, the epoxy acrylates of formula III are further reacted, without isolation, in the same reactor to the derivatives of formula IV modified with carboxyl groups.
Isolation and purification of the novel carboxyl group-containing epoxy acrylates of formula IV is usually not necessary. The reaction solution can be further used as obtained in the synthesis.
Owing to the unsaturated groups present in the molecule, the epoxy acrylates of formula III and the carboxyl group-containing epoxy acrylates of formula IV are thermally and photochemically crosslinkable in the presence of a photoinitiator such as Irgacure(copyright) 907 (2-methyl-1-[4-(methylthio)phenyl]-2-monpholino-propane-1), or any of the other photoinitiators described in U.S. Pat. No. 5,942,371 (as incorporated by reference below) at column 9, line 46 to column 10, line 14. They can therefore be used and applied as acrylate components in photoresist formulations for the production of solder resists or primary resists by known methods, as for example disclosed in Swiss patent application 2005/93-4, filed on Jul. 2, 1993, entitled xe2x80x9cPhotopolymerisable compositionsxe2x80x9d (the U.S. counterpart of which issued as U.S. Pat. No. 5,942,371 on Aug. 24, 1999 hereby incorporated by reference), and give resist layers having enhanced thermal, mechanical, electrical and chemical properties. The resist formulations prepared therefrom are used in particular in the field of printed wiring boards as solder resists or primary resists, and of printing plates. They are also suitable for the production of offset printing plates, flexographic printing plates, book printing plates and screen printing formulations. Suitable developers are aqueous as well as aqueous-organic or organic systems. Owing to the presence of carboxyl groups in the compounds of formula IV, these systems are particularly suitable for the preparation of aqueous-alkaline developable photoresists.
Compared with low molecular epoxy acrylates in formulations that contain polymer binders, it is suprising that formulations containing epoxy acrylates of higher molecular weight without the addition of such polymer binders bring about an enhancement and not a loss of photosensitivity, and also that no increase in tackiness results. Furthermore, use of the formulations as solder resists results in improved edge coverage of the conductors. As no additional polymer binders are used in such formulations, further advantages accrue with respect to the thermal, mechanical and electrical properties and, in particular, to the resistance to chemicals of the resist compositions prepared therefrom. The novel epoxy acrylates of formula III and the carboxyl group-containing epoxy acrylates of formula IV have an increased glass transition temperature.
The invention is illustrated by the following non-limitative Examples.